The subject of this invention is a static gasket designed to be used mainly in the automotive field and to make a tight seal between an immobile part and a cover, for example of an oil tank, a cylinder head, an oil pump or a water pump, or to make a tight seal on a distributor case, or to form an intake manifold seal.
There are different types of static gaskets at this time.
A first gasket is made of pure elastomer. This gasket has the advantage of being cheap and having damping properties. However, this gasket has no mechanical stability before mounting, and the center distance between the axes of the holes the screws go through is not controlled, which complicates handling and mounting. This type of gasket also has no compression limits and does not ensure any fixed dimension between the elements being sealed, unless there are struts, which can translate into risks of bursting in the tightened position.
A second gasket is made from a silicone paste deposited directly on the container to be sealed. This type of gasket is used mainly for cylinder head covers. In this case, a bead of paste is deposited by a robot on an assembly line. The advantage of such a gasket is that it is cheap, its basic disadvantages being that it is destroyed when the cover with which it is associated is removed, and that it is difficult to redeposit a new gasket like it.
Another type of gasket is comprised of a cardboard support (fiber and elastomer) produced by paper manufacturing techniques. Such gaskets are used frequently to make seals on oil tanks and sometimes cylinder head covers. Such a gasket has the advantage of being cheap, but it makes a very mediocre seal.
Another type of gasket is the coated metal type. This is a band of metal material, such as stainless steel, approximately 0.2 to 0.4 mm thick, which has at least one continuous rib to provide the stress that makes the seal. To protect the steel, this metal band is coated with a layer of several microns of elastomer, such as a nitrile or a fluorine-type elastomer forming a surface-sealing layer.
Such a gasket has a reasonable cost price, has good sealing properties, but takes substantial resources to produce (induction line).
Document U.S. Pat. No. 4,625,979 concerns a cylinder head gasket having a core made of several laminated layers, for example a metal core coated on its two faces with two fibrous layers, fiberglass or asbestos-based, bonded by a polymer. The holes the fluids go through are surrounded by beads of silicone seal with a constant height, deposited by serigraphy and each bordered, on both sides, by a more rigid rib, designed to limit the flow of the silicone bead when tightened.
The goal of the invention is to provide a static gasket at a moderate cost price that is easy to use and suitable for many applications.
For this purpose, the gasket that it concerns, has a flat metal core made of soft steel, coated on each side with an elastomer layer bonded with components that allow it to adhere to the metal, with the thickness of the elastomer varying on the surface of the gasket, depending on the shape of the pieces between which the gasket is intended to be mounted and the sealing requirements at each point on the surface of the gasket; the elastomer is deposited cold on each side of the gasket, then the whole thing is placed in a heated mold, designed to mold the elastomer and then vulcanize it.
One feature of the invention is that the soft steel of which the core is composed is galvanized steel, and the thickness of the core is around 0.2 mm. The elastomer can be in the silicone family.
The invention thus provides a gasket in which the sealing parts made of elastomer are made of a single material and obtained in a single operation, during the manufacture of the gasket, with modulation of the thickness to guarantee a contact pressure adapted to the potential deformation of the pieces being sealed. Considering the presence of the adhering compounds, the resistance of the elastomer to the lateral flux under stress is excellent, and the whole thing can resist pressures of 80 MPs.
Another feature is that the thickness of the elastomer can vary from 0 to 0.3 mm per face.
In addition, each layer of elastomer contains, at least locally, a thread or rib extending in the direction of the length of the gasket. Each thread has a section with a general triangular shape, and the height of the threads can vary depending on the seal being made, based on the tightening characteristics. The height of the threads can be around 0.06 to 0.5 mm. The thread can be either not present at certain places on the gasket, or it is possible to have several parallel threads in other places to create several sealing barriers.
In one embodiment, each layer of elastomer has, at least locally, crossed threads forming a network that partitions off the seal.
Another feature of the invention is that at least one layer of elastomer has localized excessive thickness near at least one of its edges to make a lateral seal when tightened.
Another possibility is that the metal core has clefts forming tightening stops that improve the connection of the elastomer layers.
In any case, the invention will be better understood from the following description, which refers to the attached schematic drawing showing one form of embodiment of this gasket as a non-limiting example.